GB1585187A

GB1585187A - Sheet turner

Info

Publication number: GB1585187A
Application number: GB52299/77A
Authority: GB
Original assignee: SOLNA OFFSET AB
Current assignee: SOLNA OFFSET AB
Priority date: 1976-12-21
Filing date: 1977-12-15
Publication date: 1981-02-25
Also published as: IT1091920B; JPS5735112B2; FR2375045B3; SE7614362L; FR2375045A1; DE2756507A1; JPS5379607A

Description

(54) SHEET TURNER (71) We, SOLNA OFFSET AB, a Swedish Body Corporate, of Knistavägen 21, S-191 47 Sollentuna, Sweden, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to a sheet turner, preferably for use in offset presses.

In offset printing the printing surface consists of a thin plate which is chemically treated so that it attracts water on the nonprinting surfaces and ink on the printing surfaces. The plate is fastened onto a plate cylinder, and ink and damping water are continuously applied to the plate during printing. The image is transferred from the printing plate to a rubber blanket tensioned on the blanket cylinder and from there the actual printing is done on the paper.

The printing paper is transported from the stack of paper into the press and is gripped by the counter-pressure cylinder which presses the paper against the blanket cylinder with the image. Printing against a counter-pressure cylinder is most common in sheet offset presses. The paper lies on the outside of the counter-pressure cylinder and is pressed while curved against the rubber blanket. Instead of merely printing one side of a paper, both sides can be printed simultaneously, with two blanket cylinders acting against one another.

This is especially common in web offset presses but also occurs in sheet presses.

For printing in several colors, multicolor presses are usually constructed according to two different principles, either as so-called unit presses or with the use of a common counter-pressure cylinder. In unit presses the sheet is picked up from the feeder pile by the suction head, air is blown under the sheet and it is fed forward to conveyor belts which transport it to the register table where it is registered from the front and from the side as it remains momentarily completely stationary. The sheet is then accelerated by some form of mechanism, whose construction varies considerably in different presses, to the same velocity as the counter-pressure cylinder at the moment when the sheet is drawn in by its grippers into printing engagement.

From the counter-pressure cylinder the paper is given to an intermediate cylinder, and it is held momentarily by the grippers on the counter-pressure cylinder as well as the grippers on the intermediate cylinder. Depending on the design of the press, there are one or three intermediate cylinders between each printing unit. Especially in presses with several intermediate cylinders between the units, the paper will pass a large number of gripper changes as it is fed through the press.

During the actual changing of the grippers, the grippers on one cylinder will press the paper against its gripper pads, while the grippers on the other cylinder will take the paper between the first grippers and press it over against its own gripper pads. The operation of the grippers is controlled by mechanical cams which are very exactly designed and made with small tolerances. Normally, the paper moves about 3 mm while being held by both sets of grippers.

In sheet transfer it can also be desirable to turn the sheet with a so-called sheet turner.

The sheet is gripped at its rear edge instead of at its front edge by the grippers of the sheet turner.

In multicolor presses with a common counter-pressure cylinder, the sheet is moved to and from the press in the same manner as in unit presses, but during the printing the sheet is held against a single counter-pressure cylinder for the first as well as the second color. The sheet is then usually taken over by a gripper trolley, which is moved by chains over to the next printing unit, where the third and fourth colors are applied, and then possibly by chains again to another unit for the fifth and sixth colors.

Reducing appreciably the number of changes of grippers reduces the risk of deformation of the paper during the change of grippers, but on the other hand there are problems in registering the trolley which moves the sheet from one printing unit to another.

All of these problems are eliminated in web offset presses, but there are problems with keeping the paper tension constant in the paper web, and in printing in several successive colors there are strict requirements on the evenness of the web tension.

After printing, the sheets or web is/are moved out of the press for drying and completion.

It can be necessary at times to turn the sheet over with a sheet turner between two intermediate rollers for, for example, "shown und wider" printing (printing on both sides) in a two color press. Thus the register when printing the reverse side will be from the rear edge and may be somewhat inexact, but with the present sheet turner it is entirely satisfactory for common black printing, for example, According to the invention there is pro vided a method of turning over a sheet in a sheet printing press, in which a swinging gripper is coupled in between two intermediate rollers to grasp a sheet at its rear edge on a first of the intermediate rollers and transfers it to the other intermediate roller with the former rear edge as the new forward edge, characterized in that the direction of movement, speed, and the opening and closing of the swinging gripper are controlled so that the swinging gripper grips the rear edge of the sheet on the first intermediate roller while moving with the same speed as said roller, retards the speed of the sheet to zero, changes the direction of movement of the sheet and accelerates the sheet to the same speed as the other intermediate roller, inserts the sheet in the roller grippers of said other intermediate roller, opens, releases the sheet, decelerates to a standstill while closing the roller grippers, changes its direction of movement and accelerates to the same high speed as the first intermediate roller, said first intermediate roller being caused to decrease its radius when the swinging gripper passes, as well as when the roller grippers of said other intermediate roller pass and open, for grasping the rear edge of the sheet from the swinging gripper.

Also according to the invention there is provided a sheet turner for turning over sheets in a printing press, bookbinding machine or the like comprising a swinging gripper on a shaft arranged between two intermediate rollers to grasp the rear edge of a sheet from the gripper of one of the intermediate rollers, change the direction of movement of the sheet, and deliver it to the grippers of the other intermediate roller under the control of a control device, characterized in that the grippers in the first intermediate roller are mounted in a swingable segment of the first roller casing, and said segment is retractable into the first roller away from the path of movement of the swinging gripper.

The. sheet turner will be described in more detail in connection with the accompanying drawings of which Fig. 1 shows a schematic representation of a sheet press for offset printing, Fig. 2 a common sheet transfer from one roller to another, Figs. 3a-f show a sheet turner according to the invention at different points in its movement, and Fig. 4 shows an intermediate roller according to the invention in perspective.

Fig. 1 shows schematically an offset sheet press with four printing units, 1, 2, 3, 4. The paper 6 gqes from the paper stacks over the register table 7 to other first printing unit 1, where it is pressed between the counterpressure cylinder 8 and the blanket cylinder 9. The plate cylinder 10 is inked from an inking unit 10a and is damped from a damping unit lOb.

After printing with the first color the paper is transported via the intermediate rollers 11, 12 and 13 to the next printing unit 2, is printed with the second color between the counter-pressure cylinder 18 and the blanket cylinder 19, is transported to printing unit 3 by intermediate cylinders 21, 22 and 23, etc.

After printing in the last printing unit 4, the finally printed paper is laid on the stack 14.

Fig. 2 shows schematically the transfer of a sheet 6 from one roller to another, for example from intermediate roller 13 to counter-pressure cylinder 18. The sheet is held by the grippers 15 of the intermediate roller 13 and is drawn into the grippers 16 of the counter-pressure cylinder 18. For a very short distance, about 3 mm, the paper is held by both grippers 15 and 16. Grippers 15 then open and the paper is pulled on by the grip pers 16 and the counter-pressure cylinder 18 To enable the grippers to open wthout colliding with the adjacent roller, the grippers are recessed in channels 17 in the respective rollers and do not project when closed beyond the casing surface of the roller.

The grippers are controlled by mechanical cams (not shown) in a control sequence which must be very exact and synchronized with the rotation of the cylinders.

When sheet turning is to be employed, a sheet turner is mounted between two intermediate cylinders between two printing units.

Figs. 3a-f show sheet turning between the second intermediate cylinder 22 and the third intermediate cylinder 23 between print ing units 2 and 3 for printing 2+2 colors in a four-color press.

A sheet of paper 6 from the first intermediate cylinder 21 is grasped by the grippers 24 -on the second intermediate cylinder 22 and is held while the cylinder rotates forward to the position shown in Fig. 3a. In this position, a swinging gripper 25, journalled on the shaft 26, swings in the direction of the arrow 27 into eontact with the rear edge of the sheet 6 and the moving part 28 of the gripper opens away from the stationary part 29 of the gripper. The speed of the swinging gripper is greater than that of the intermediate cylinder 22, but the swinging movement is retarded so that the speed of the gripper opening is the same as that of the sheet when they make contact. The gripper opening 28, 29 closes simultaneous with, or a couple of mm before, the opening of the gripper 24 on the intermediate cylinder 22.

The swinging gripper continues its movement a short distance at the same time as its speed is reduced, and at the moment when it takes the paper its speed is the same as that of the sheet of paper, Fig. 3b. Fig 3c shows the open gripper 24 on intermediate cylinder 22 moving away after having released the now stationary sheet 6 which is held fast by the gripper 25 at its lower turning-point, as the next sheet 6a on the intermediate cylinder 22 is being brought down.

At the lower turning-point the direction of movement of the gripper 25 is reversed and it swings upwards with increasing speed, as shown in Fig. 3d. The grippers 40 of the intermediate cylinder 23 are open and are ready to accept the sheet 6 which is drawn by the swinging gripper into the gripper 40.

A sheet guide 41 is disposed between the rollers 22, 23 and the swinging gripper 25, and is fed momentarily or continuously with compressed air to catch the sheet 6 and guide it to prevent flapping and smearing.

The grippers 24 of the intermediate cylinder 22 have released the sheet and are on their way up again to receive a new sheet from intermediate cylinder 21.

Fig. 3e shows how the sheet is held by both the swinging gripper 25 and the cylinder gripper 40 after the sheet has been imparted at a speed which corresponds to that of intermediate cylinder 23. The speed of the swinging gripper 25 at the moment when the sheet is taken is the same as that of the intermediate cylinder 23, and the sheet guide 41 keeps the sheet on the correct path. The swinging gripper delivers the sheet and continues to its upper turning-point (Fig. 3f) while the gripper itself 28 opens and the speed successively drops to zero. The direction of movement of the swinging gripper 25 is reversed, the movable gripper member 28 closes and the speed is successively increased as it returns.

The cycle is repeated and the swinging gripper 25 again approaches the intermediate cyclinder 22, is brought up to the same speed as it, the movable gripping member 28 opens to grasp a new sheet 6 on intermediate cylinder 22 according to Fig. 3a and so on.

It has been shown that there is a risk that the swinging gripper during a portion of its movement runs the risk of colliding with the intermediate roller from which it grasps the sheet and thus being damaged.

This is remedied by making the intermediate roller from which the swinging gripper takes the sheet so that its radius can be reduced during a portion of the rotation, thus giving the swinging gripper free clearance.

To enable a gripper on a roller to deliver a sheet to the corresponding gripper on the next roller without collision, the grippers, as was mentioned previously, are recessed in channels 17. The intermediate cylinders move synchronously with one another and the construction works excellently for common sheet exchange. The swinging gripper 25 has, however, a reciprocating movement in order to grasp the rear edge of the sheet 6 on the intermediate cylinder 22. A corresponding gripper channel cannot be arranged on the intermediate cylinder because sheets of different lengths are printed on different occasions.

To enable the moving gripping member 28 while open to pass the intermediate cylinder 22 and reach the back edge of the sheet, the intermediate cylinder has been made with a variable diameter, i.e. with the casing composed of segments, one or more of which are movable and provided with grippers, while other segments are fixed and define a constant cylinder radius which is the same as that of the two other intermediate cylinders 21 and 23.

The cylinder grippers 24 and 24a on the intermediate roller 22 each consist of an upper moving gripping member 50 which acts against a fixed stop 51. The moving gripper member is swingable around a shaft shaft 52 which is in turn journalled on a fixed shaft 54, mounted in a channel 55 in the cylinder. The channel 55 has sufficient width to accommodate the entire movable segment 53 when it makes a limited swing movement around the shaft 54 and is thus retracted into the cylinder. In the extended position the movable segment(s) 53 are aligned with the fixed portion(s) of the cylinder casing, and by switching off the retraction control, the intermediate cylinder 22 can be used for usual transmission of sheets without turning.

The perspective representation of the roller 22 in Fig. 4 shows the cylinder member 53 retracted into the channel 55 and with the grippers 24 open, corresponding to the position when a sheet has just been delivered to the swinging gripper.

Additional problems arise with sheet turning due to the fact that collisions can also occur between the grippers 24 on the intermediate cylinder 22 and the corresponding grippers on cylinder 23. The movement of the swinging gripper 26 is synchronized with the rotation of the cylinder 22 so that they have parallel cycles of movement. However, due to the varying lengths of the sheets 6, the cycles of movement must be shifted in relation to one another so that the lower turning point of the swinging gripper coincides with the passing of the rear edge of the sheet. The cycle of movement for cylinder 23 must then be adjusted in agreement with the setting of the cycle of movement of the swinging gripper, so that the grippers of cylinder and the swinging gripper meet at the upper turning point of the swinging gripper. This means that the cycles of the cylinders 22 and 23 may need to be shifted significantly in relation to one another due to the length of the sheet, and the grippers and the sheet would then come into a collision position with one another.

This problem does not, of course, arise in normal sheet transfer, only in sheet turning.

In normal sheet transfer the grippers act on the forward edge of the sheet, and the length of the sheet and the position of the rear edge are irrelevant to the sequence of movements.

By retracting the grippers on cylinder 22 at A and extending them at B, these grippers will clear cylinder 23 completely, and likewise the grippers on cylinder 23 will have free clear ance above the moving member 53 on cylinder 22.

Thus by using the swinging gripper in a two color press, alternating with two-color printing, two sides of a sheet can be printed in black, or, in a four-color press, 2+2 colors can be printed, or possibly 2 + 1 or 3 + 1 colors, etc.

When using the sheet turner, the swinging gripper is coupled in via a gear box to the synchronized intermediate cylinders for driv ing. Mechanical cams or mechanisms control the speed, direction of movement, and open ing and closing of the swinging gripper.

Mechanical controls of this type are well known in printing technology and are there fore not described in more detail here. Mech anical controls which are easily installed can be manufactured with very high precision, and for simple engagement and disengagement of the swinging gripper, the gear box can be permanently mounted in the press so that only the swinging gripper itself is removed when the sheets are not to be turned.

Even electronic or hydraulic control of the swinging gripper is possible and tests with pneumatic control have also shown good results.

WHAT WE CLAIM IS 1. Method of turning over a sheet in a sheet printing press, in which a swinging gripper is coupled in between two intermediate rollers to grasp a sheet at its rear edge on a first of the intermediate rollers and transfer it to the other intermediate roller with the former rear edge as the new forward, characterized in that the direction of move ment, speed, and the opening and closing of the swinging gripper are controlled so that the swinging gripper grips the rear edge of the sheet on the first intermediate roller while moving with the same speed as said roller, retards the speed of the sheet to zero, changes the direction of movement of the sheet and accelerates the sheet to the same speed as the other intermediate roller, inserts the sheet in the roller grippers of said other intermediate roller, opens, releases the sheet, decelerates to a standstill while closing the roller grippers, changes its direction of movement and accelerates to the same high speed as the first intermediate roller, said first intermediate roller being caused to decrease its radius when the swinging gripper passes, as well as when the roller grippers of said other intermediate roller pass and open, for grasping the rear edge of the sheet from the swinging gripper.

2. Method according to Claim 1, characterized in that the swinging gripper is controlled mechanically according to control cams.

3. Method according to Claim 1, characterized in that the swinging gripper is controlled electronically.

4. Method according to Claim 1, characterized in that the swinging gripper is controlled hydraulically.

5. Method of turning over a sheet in a sheet printing press substantially as hereinbefore described.

6. Sheet turner for turning over sheets in printing press, bookbinding machine or the like comprising a swinging gripper on a shaft arranged between two intermediate rollers to grasp the rear edge of a sheet from the gripper of one of the intermediate rollers, change the direction of movement of the sheet, and deliver it to the grippers of the other intermediate roller under the control of a control device, characterized in that the grippers in the first intermediate roller are mounted in a swingable segment of the first roller casing, and said segment is retractable into the first roller away from the path of movement of the swinging gripper.

7. Sheet turner according to Claim 6, characterized in that the swingable segment is arranged in a channel in the intermediate roller.

8. Sheet turner according to Claim 6, characterized in that the control device is mechanical.

9. Sheet turner according to Claim 6, characterized in that the control device is electronic.

10. Sheet turner according to Claim 6, characterized in that the control device is hydraulic.

11. Sheet turner according to Claim 6, characterized in that a sheet guide is disposed between the intermediate rollers and the swinging gripper to guide the sheet and prevent flapping and smearing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the varying lengths of the sheets 6, the cycles of movement must be shifted in relation to one another so that the lower turning point of the swinging gripper coincides with the passing of the rear edge of the sheet. The cycle of movement for cylinder 23 must then be adjusted in agreement with the setting of the cycle of movement of the swinging gripper, so that the grippers of cylinder and the swinging gripper meet at the upper turning point of the swinging gripper. This means that the cycles of the cylinders 22 and 23 may need to be shifted significantly in relation to one another due to the length of the sheet, and the grippers and the sheet would then come into a collision position with one another. This problem does not, of course, arise in normal sheet transfer, only in sheet turning. In normal sheet transfer the grippers act on the forward edge of the sheet, and the length of the sheet and the position of the rear edge are irrelevant to the sequence of movements. By retracting the grippers on cylinder 22 at A and extending them at B, these grippers will clear cylinder 23 completely, and likewise the grippers on cylinder 23 will have free clear ance above the moving member 53 on cylinder 22. Thus by using the swinging gripper in a two color press, alternating with two-color printing, two sides of a sheet can be printed in black, or, in a four-color press, 2+2 colors can be printed, or possibly 2 + 1 or 3 + 1 colors, etc. When using the sheet turner, the swinging gripper is coupled in via a gear box to the synchronized intermediate cylinders for driv ing. Mechanical cams or mechanisms control the speed, direction of movement, and open ing and closing of the swinging gripper. Mechanical controls of this type are well known in printing technology and are there fore not described in more detail here. Mech anical controls which are easily installed can be manufactured with very high precision, and for simple engagement and disengagement of the swinging gripper, the gear box can be permanently mounted in the press so that only the swinging gripper itself is removed when the sheets are not to be turned. Even electronic or hydraulic control of the swinging gripper is possible and tests with pneumatic control have also shown good results. WHAT WE CLAIM IS

1. Method of turning over a sheet in a sheet printing press, in which a swinging gripper is coupled in between two intermediate rollers to grasp a sheet at its rear edge on a first of the intermediate rollers and transfer it to the other intermediate roller with the former rear edge as the new forward, characterized in that the direction of move ment, speed, and the opening and closing of the swinging gripper are controlled so that the swinging gripper grips the rear edge of the sheet on the first intermediate roller while moving with the same speed as said roller, retards the speed of the sheet to zero, changes the direction of movement of the sheet and accelerates the sheet to the same speed as the other intermediate roller, inserts the sheet in the roller grippers of said other intermediate roller, opens, releases the sheet, decelerates to a standstill while closing the roller grippers, changes its direction of movement and accelerates to the same high speed as the first intermediate roller, said first intermediate roller being caused to decrease its radius when the swinging gripper passes, as well as when the roller grippers of said other intermediate roller pass and open, for grasping the rear edge of the sheet from the swinging gripper.

12. Sheet turner for turning over sheets

in a printing press, bookbinding machine or the like substantially as hereinbefore described with reference to the accompanying drawings.